Multi-tap distribution apparatus

ABSTRACT

A distribution apparatus is provided which, if a short circuit occurs in a secondary line from a branch output terminal of the apparatus or in terminal equipment connected to the secondary line, stops supplying electric currents to the concerned branch output terminal. In the distribution apparatus, external taps (22) which serve as distribution output terminals are connected to a current passage network (26). A positive thermistor (27) is connected to each external tap (22) in the current passage network (26).

FIELD OF THE ART

The present invention relates to a multi-tap distribution apparatus.More particularly, the present invention relates to a multi-tapdistribution apparatus which is suitable for use with CATV cables.

BACKGROUND ART

Generally, CATV transmission cables are connected to subscribers viamulti-tap distribution apparatuses. CATV stations transmit through thecables not only television signals and control signals but also currentsfor operating main line amplifiers. Therefore, some distributionapparatuses are designed for passing electrical currents therethrough.

Handling instructions and precautions for equipment connected to thetransmission cable are not often followed at subscribers' homes. Forexample, equipment may be inappropriately installed or tampered with bychildren, which often causes a short circuit. If a short circuit occursin a secondary line branching out of a terminal of a branch circuit of adistribution apparatus or in terminal equipment connected to thesecondary line, it can cause damage not only to the distributionapparatus to which the concerned secondary line is connected but also tothe circuits of the equipment installed in the main line.

A fuse or bimetal device is sometimes interposed in the currenttransmission circuit of a distribution box to block the transmission ofa large current. However, replacing a fuse to restore the flow ofcurrents is a time-consuming task as it requires opening thedistribution apparatus. On the other hand, the problem with the bimetaldevice is that, having a high calorific value, this device tends toraise the temperature in the distribution apparatus and hence change thecharacteristics of the ferrite components inside.

DISCLOSURE OF THE INVENTION

The present invention provides for a distribution apparatus the currenttransmitting function of which is immediately lost upon occurrence of ashort circuit at a terminal of the transmission cable, but isautomatically restored when the cause of the short circuit is removed.The distribution apparatus is characterized in that its branch outputterminals and the transmission cable can be connected to each other by acurrent passage network which has positive thermistors interposedtherein.

Preferably, one positive thermistor is provided for each of the outputbranch terminals in the current passage network.

Also, the connection state of said current passage network can beselected by switching operation.

In one aspect of the invention, the positive thermistors may beconnected to the current passage network via connectors by beingdetachably coupled to the connectors. In this way, the connection stateof said current passage network can be selected by detaching orattaching the thermistors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a multi-tap distributionapparatus of an embodiment of the present invention.

FIG. 2 shows a plan view of the components of the multi-tap distributionapparatus.

FIG. 3 shows the circuit diagram of the components of the multi-tapdistribution apparatus.

FIGS. 4A, 4B and 4C show different pairs of cable connecting portions toserve as the input and output terminals for the transmission cables.

FIG. 5 shows the circuit diagram of a modified distribution apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

A multi-tap distribution apparatus embodying the present invention willbe explained with reference to the attached drawings. The multi-tapdistribution apparatus of the embodiment can be used as either an aerialtype or pedestal type device. Also, the number of taps can be changed inthe distribution apparatus of this embodiment.

Referring to FIGS. 1 to 3, numeral 1 designates a box-shaped housingwith one side open. The housing 1 is provided with one cable connectingportion 2 on one end surface and two other cable connecting portions 3and 4 on the opposite end surface. Each of the cable connecting portions2, 3, and 4 is disposed on a corner of the housing 1. Connectorinsertion holes 2a, 3a, and 4a are provided in the end surfaces.Provided in the longitudinal sides of the housing 1 are three screwaccess holes 2b, 3b, and 4b for connecting the central conductors of theconnectors to the cable connecting portions 2, 3, and 4 .

The housing 1 has in its center a mounting area 5 on which three mainline connection terminals 5a, 5b, and 5c are provided. The upperterminals 5a and 5b are located above, and on the right and left sidesof, the center P of the housing 1 while the terminal 5c is locateddirectly under the right terminal 5b. The terminals 5a, 5b, and 5c areconnected to the respective cable connecting portions 2, 3, and 4,respectively, via transmission lines 30, 31, 32. Each transmission line30, 31, 32 is composed of a central conductor inserted through a metalcylinder called a coaxial tube.

Being constructed in this manner, the transmission line 30, 31, 32 has alayer of air between the central conductor and the outer conductor. Thisstructure reduces the diameter of the coaxial tube so as to cause only asmall transmission loss. It is also confirmed that to obtain the sameeffect, grooves with a semi-circular cross section may be formed in theinner surface of the housing instead of using the coaxial tubes.

Reference numeral 6 is a mother board having a pair of transmissionterminals 7 on its rear face and a pair of relay terminals 8 on itsfront face. The transmission terminals 7 are spaced apart so as tocorrespond with the main line connection terminals 5a and 5b (or 5b and5c). Each of the transmission terminals 7 is connected to a relayterminal 8 via a high-frequency passing circuit 9 with a capacitor 9ainterposed therein. The circuits 9 allow high-frequency signals to passtherethrough. The two transmission terminals 7 are connected to eachother by a current transmission circuit 10 with a coil 10a interposedtherein.

Also, the housing 1 has a plurality of guide pins 11 projected therefromwhile the mother board 6 has a plurality of guide holes 12 formedtherein corresponding to the guide pins 11. The mother board 6 ismounted in the housing 1 by inserting the guide pins 11 into the guideholes 12. In this way, the transmission terminals 7 are easily alignedand brought into contact with, for example, the main line connectionterminals 5a and 5b, although these terminal are not visible behind themother board 6 during mounting. Then, the mother board 6 is secured tothe housing 1 with a pair of screws 13.

Also, the mother board 6 has a pair of engaging slits 14 formed thereinoutside the relay terminals 8.

Reference numeral 15 designates a box-shaped branch unit which has onone surface a pair of connection terminals 16 and 16' which correspondto the relay terminals 8 of the mother board 6. The branch unit 15 hason the opposite surface a branch terminal 17. The connection terminals16 and 16' and the branch terminal 17 are connected to a built-in branchcircuit. With the connection terminal 16 serving as the input terminaland the connection terminal 16' serving as the output terminal, thebranch unit 15 can convey high-frequency signals in a predetermineddirection. It also has on both ends thereof two engaging claws 18projected toward the surface where the connection terminals 16 and 16'are located. When the branch unit 15 is mounted on the mother board 6 byengaging the claws 18 with the slits 14, the connection terminals 16 and16' are brought into contact with the relay terminals 8.

The branch unit 15 may be mounted on the mother board 6 by othermethods. For example, the engaging claws formed on the branch unit maybe replaced with guide lugs which are inserted into the slits formed inthe mother board. Furthermore, screws or clips may be employed as themeans of mounting the branch unit on the mother board.

The mother board 6 is provided with a push switch 19. When the branchunit 15 is mounted on the mother board 6, the outer surface of thebranch unit 15 presses against and turns off the switch 19. When thebranch unit 15 is detached from the board mother 6, the push switch 19is released from the pressure of the unit 15 and turned on, thusshort-circuiting the relay terminals 8 and allowing passage ofhigh-frequency signals between the transmission terminals 7.

Moreover, the current transmission circuit 10 of the mother board 6ensures that currents and high-frequency signals flow between thetransmission terminals 7 whether or not the branch unit 15 is mounted onthe mother board 6.

Reference numeral 20 is a tap board mounted on the inner surface of amain body 21. The tap board 20 includes a distributing circuit and fourexternal taps 22 exposed on the outer surface of the main body 21. Theexternal taps 22 serve as distribution output terminals. The tap board20 also has on its inner surface an input terminal 23 corresponding tothe branch terminal 17 of the branch unit 15. Additionally, the housing1 is provided with a current passage contact 24 which is connected tothe cable connecting portion 3 while the main body 21 is provided withanother current passage contact 25 which is connected to thedistributing circuit of the main body. Therefore, currents can betransmitted through these two contacts. The current passage contact 24is connected to the external taps 22 via a current passage network 26provided on the tap board 20. By fitting the main body 21 on the housing1, the branch terminal 17 is brought into contact with the inputterminal 23. At the same time, an electrical contact is also establishedbetween the current passage contacts 24 and 25.

The current passage contact 25 is of a pin type biased toward the tipthereof by a coil spring. The current passage contact 25, if shifted offthe insertion-type current passage contact 24, moves back whilecompressing the coil spring, thus preventing breakage thereof. However,when the housing 1 is moved with respect to the main body 21 to alignthe two contacts, the contact 25 projects forward to establish anelectrical contact.

A positive thermistor 27 (model name: Polyswitch RXE0675; manufacturedby Reikem) is interposed between the contact 25 and each distributionoutput terminal via a connector 28 in the current passage network 26.The positive thermistors 27 can be easily coupled to and detached with asingle motion from the connectors 28 (model name: VH series connector;manufactured by Nippon Solderless Terminal Corporation).

As shown in FIG. 4A, the multi-tap distribution apparatus can be used asan aerial type device when the branch unit 15 is mounted on the motherboard 6 with the terminal 16 on the same side as the cable connectingportion 2 and the terminal 16' on the same side as the cable connectingportion 3. In this case, the cable connecting portion 2 is used as theinput terminal while the cable connecting portion 3 is used as theoutput terminal.

The positions of the input and output terminals can be easily reversedby detaching and horizontally rotating the branch unit 180 degrees andmounting it back on the mother board 6 (see FIG. 4B).

To use the multi-tap distribution apparatus as a pedestal type device,the mother board 6 is detached and rotated 90 degrees in clockwisedirection as shown in FIG. 4C, so that the connection terminals 16 and16' are connected with the main line connection terminals 5b and 5c viathe transmission terminals 7. In this application, the cable connectingportion 3 serves as the input terminal and the cable connecting portion4 as the output terminal. The positions of the input and outputterminals can be easily reversed as in the aerial type application: bydetaching and rotating the branch unit 15 one hundred and eighty degreesand mounting it back on the mother board 6 (this position is not shown).

To change the number of branches (secondary cables), the main body 21,the tap board 20, and the branch unit 15 are replaced with a differentmain body incorporating a tap board having a desired number of taps anda different branch unit.

To perform such a replacement, the branch unit 15 can be easily detachedby disengaging the claws 18 from the slits 14. Upon detachment of thebranch unit 15, the switch 19 is turned on, thus short-circuiting thetransmission terminals 7 and maintaining high-frequency signaltransmission between the cable connecting portions. Accordingly, thehigh-frequency signal transmission remains uninterrupted while thebranch unit 15 is replaced.

In this embodiment, different cable connecting portions can be selectedfor use as the input and output terminals by rotating the mother board90 degrees. Also, the number of taps can be increased or decreased byreplacing the branch unit and the main body. Not only does thisconstruction improve the operability of the multi-tap distributionapparatus, but it also allows the multi-tap distribution apparatus to beused as an aerial or pedestal type. Moreover, the multi-tap distributionapparatus offers the advantage of maintaining the check function from aremote site even when the branch unit or the main body is removed sincethe transmission of the currents and the high-frequency signals from theinput side to the output side remains uninterrupted.

If the transmission cable is used as a telephone line, telephoneconversations are not interrupted by using the current transmissioncircuit and the telephone line as the telephone uses signals in thelow-frequency range.

If a short circuit occurs on the distribution output terminal side, theresistance of the positive thermistor included in the current passagenetwork increases from tenths of an ohm to several kilo ohms, thusblocking the current flow between the cable connecting portion and thedistribution output terminal. This protects the circuits in thedistribution apparatus while preventing damage to equipment and devicesconnected to the transmission cable. This structure can be safely usedin applications where currents of 15 amperes or more are conveyed.

As explained above, the high-frequency transmission circuit (branchcircuit) is installed separately from the current passage network and apositive thermistor is connected to each distribution output terminal.Therefore, if a short circuit occurs, the current flow is interruptedonly to the concerned branch output terminal while maintainingtransmission of the television signals.

Since a positive thermistor is detachably connected to each externaltap, it is possible to leave installed the positive thermistors for theexternal taps connected to the subscribers using telephone lines forreceiving CATV services. Meanwhile, the power supply can be easilystopped to non-subscribers by removing from the connectors the positivethermistors for the external taps which are connected tonon-subscribers. Not only can this operation be simply done but also itis easy to recognize to which externals taps currents are carried.

Alternatively, as shown in FIG. 5, the same result can be obtained byproviding switches 29 in the current passage network 26 and selectivelyturning on and off the switches 29 instead of detaching positivethermistors as explained above.

Instead of inserting coaxial cables through the cable insertion holesand connecting the cable conductors to the cable connecting portionswith screws, connectors may be used to couple the cables.

Each cable connecting portion may be provided with only one cableinsertion hole or connector. Furthermore, the number of taps may beeither increased or decreased; the main body may have any number oftaps.

As described above, the embodiment includes three main line connectionterminals on the inner surface of the housing. Two of the terminals arelocated above and on both sides of the center of the housing while thethird terminal is located directly under one of the upper terminals.Accordingly, the pair of main line connection terminals of the motherboard to be connected with the transmission terminals can be selected byrotating the mother board. Instead of this construction, equally spacedpairs of main line connection terminals may be arranged on the housingso that the transmission terminals are connected to any desired pair ofmain line connection terminals by shifting the mother board. However,the present invention is applicable to the types of models in which mainline connection terminals cannot be selected for connection or thenumber of external taps cannot be changed.

If only protection of the components and equipment from short circuitsis desired, only one positive thermistor needs to be interposed in thecurrent passage network near the main line connection terminal.

EFFECT OF THE INVENTION

According to the invention, the cable connecting portions and thedistributing circuit of the main body are interconnected by a currentpassage network via positive thermistors. Thus, if there is a shortcircuit on the external tap side, the resistance of the positivethermistors increases, thus blocking the current flow between the cableconnecting portion and the distribution output terminal. This protectsthe circuits in the distribution apparatus while preventing damage toequipment and devices connected to the main line. This feature isparticularly useful when large currents arc carried.

Moreover, the current passage network is easily connected with minimumeffort by mounting on the main body the housing which incorporatesnecessary modules. This structure makes the assembly an easy task.Further, since one thermistor is provided for each external tap, anaccident in one of the secondary lines does not affect the others. Asthe thermistors are detachably provided, some of the external taps canbe connected to house holds to which currents are to be supplied whileother taps can be connected to those to which currents are not to besupplied. Furthermore, the number of external taps can be changed inaccordance with the present invention.

We claim:
 1. A distribution apparatus for being interposed in a CATVtransmission cable, said distribution apparatus comprising,a branchcircuit means coupled to said transmission cable for distributing asoutput signals high-frequency signals received from said transmissioncable, a current passage network means coupled to said branch circuitmeans for connecting a plurality of output branch terminals of saidbranch circuit means to said transmission cable, and said currentpassage network means comprises positive thermistors coupled to saidplurality of output branch terminals of said branch circuit means. 2.The distribution apparatus in accordance with claim 1 wherein one ofsaid positive thermistors is provided for each of said plurality ofoutput branch terminals in said current passage network means.
 3. Thedistribution apparatus in accordance with claim 1 wherein the connectionstate of said current passage network means can be selected by switchingoperation.
 4. The distribution apparatus in accordance with claim 1wherein said positive thermistors are connected to said current passagenetwork means via connectors by being detachably coupled to saidconnectors.
 5. The distribution apparatus in accordance with claim 2wherein the connection state of said current passage network means canbe selected by switching operation.
 6. The distribution apparatus inaccordance with claim 2 wherein said positive thermistors are connectedto said current passage network means via connectors by being detachablycoupled to said connectors.